JP2004317976A - Light guide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light guide which has both light diffusivness on the surface and high transparency. <P>SOLUTION: The light guide is provided with a light incidence surface, a light emission surface for emitting guided light to the outside, and an observation surface formed on the side opposite to the emission surface, and the observation surface is formed into a convex curved surface. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
[Industrial applications]
The present invention relates to a light guide for a front light, which can be used for lighting a license plate of a vehicle, various liquid crystal monitors, and the like.
[0002]
[Prior art]
At present, a backlight method is generally used as an illumination method for a liquid crystal monitor of a PC or a portable information terminal. In the backlight system, illumination is performed by light from a light guide (light guide member) installed on the back side of an illumination target (for example, liquid crystal).
On the other hand, a system in which a light guide is installed on the front side (observation surface) side of an illumination target and illumination is performed by light emitted from the back surface of the light guide, that is, a front light system is also used in some applications. In this method, a light guide intervenes between the viewer and the illumination target.
[0003]
[Problems to be solved by the invention]
In the front light method, glare (reflection) due to light incident from the outside on the observation surface (surface opposite to the light emission surface) of the light guide is a problem. If the front light type light guide is applied to the illumination of the license plate of a vehicle, for example, the headlight light of the following vehicle is reflected on the observation surface of the light guide, thereby making the license plate more difficult to see, and There is a possibility that it may hinder driving. By performing light diffusion processing on the observation surface, specular reflection can be suppressed, and this can solve the problem caused by the reflected light.However, in such a method, the transparency of the light guide is reduced, and the illumination target is reduced. There is a possibility that the original purpose of the light guide to enhance visibility may not be sufficiently achieved.
[0004]
[Means for Solving the Problems]
The present invention has been made in view of the above problems, and provides the following configuration.
A light incident surface, a light emitting surface that emits the introduced light to the outside, and an observation surface formed on the opposite side to the light emitting surface,
A light guide, wherein the observation surface has a convex curved shape.
[0005]
According to the above configuration, light incident on the light guide from the outside is reflected by the observation surface having the convex curved shape. Therefore, unlike the case where the observation surface is flat, the incident light is reflected in multiple directions according to the curved surface shape of the observation surface. That is, the reflected light generated on the observation surface is efficiently diffused or scattered. Therefore, the problem that the visibility of the illumination target is reduced due to the influence of the reflected light is solved. On the other hand, in the above configuration, since the external incident light can be controlled (diffused or the like) by the observation surface itself, it is not necessary to form the light diffusion layer on the observation surface surface. That is, the design of the light guide and the illumination target can be improved by using the observation surface as a glossy surface. In addition, since a light diffusion layer for controlling external radiated light is not essential, it is possible to prevent a decrease in the transparency of the light guide due to such a light diffusion layer. As a result, a light guide having high transparency can be configured, and the visibility of the illumination target is further improved.
As described above, the light guide of the present invention has a high degree of transparency while having little problem of reflection by its surface, and is extremely suitable for front-light illumination.
Hereinafter, each member of the present invention will be described.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
The light guide has a light guide plate as a main component, and includes a light incident surface on which light from the light source is incident, a light emitting surface for emitting the introduced light to the outside, and an observation surface formed on the opposite side to the light emitting surface. Prepare. For example, a plate-shaped (hexahedral) light guide plate may be used, and a pair of surfaces having the largest area may be used as a light emitting surface and an observation surface, and any of the other surfaces (end surfaces) may be used as a light incident surface. In this case, two or more end surfaces can be used as the light incident surface.
The shape of the light guide is not limited to a plate shape, and may be, for example, a plate shape with some irregularities formed, or a substantially bar shape.
[0007]
The observation surface of the light guide has a convex curved surface shape. Typically, the entire observation surface is formed by a convex curved surface, but a region other than the convex curved surface may exist in a part. For example, in consideration of connection with another member (for example, a design cover) or a reflection mode, the peripheral portion can be formed in a planar shape, or a concave portion can be provided in the peripheral portion.
As the convex curved surface shape, various secondary curved surfaces (spherical surface, columnar surface, conical surface, spheroidal surface, paraboloid of revolution, etc.), cubic curved surface, quaternary curved surface, free curved surface and the like can be adopted. Preferably, a tertiary or higher order curved surface is employed. On the observation surface composed of such a higher-order curved surface, external light is reflected in more directions on the surface, and an excellent light diffusion effect is exhibited. The observation surface may be configured by combining convex curved surfaces having different shapes (including a case where only the curvature is different).
[0008]
The observation surface is preferably symmetrical and / or vertically symmetrical. With such a configuration, not only the outer appearance of the light guide itself is improved, but also a left-right (and / or up-down) symmetric reflection mode is obtained, so that it is preferable from an optical point of view. It becomes.
[0009]
It is preferable to use a light guide having a light emitting surface having a plan view area that can cover the entire illumination target in consideration of the size of the illumination target. In order to make the light emitting surface more compact, it is more preferable to use a light guide whose light emitting surface is substantially the same as or slightly larger than the illumination target in plan view.
It is preferable to use a light guide that is as thin as possible, as long as the effect of the light guide to irradiate the illumination target with the incident light is sufficiently obtained and there is no problem in strength. For example, the light guide can be configured using a light guide plate having a thickness of 1 mm to 15 mm. If the thickness is smaller than this, it is not preferable because sufficient mechanical strength cannot be obtained. On the other hand, if it is thicker than this, it is not preferable because it requires an unnecessary installation space when it is fixed to an object to be illuminated, and the manufacturing cost increases. The light guide can be formed by using a light guide plate having a thickness of preferably 2 mm to 10 mm, more preferably 2 mm to 5 mm.
[0010]
It is preferable to form a light reflecting layer on a surface other than the light incident surface, the light emitting surface, and the observation surface of the light guide. This is to prevent light from leaking from the surface to efficiently emit light from the light emitting surface. In addition, if a light reflection layer is provided, not only light reflection but also light diffusion can be performed, so that light diffusion in the light guide can be promoted, so that more uniform light can be emitted from the light emitting surface. Can be.
[0011]
The material of the light guide is not particularly limited as long as it is transparent to the light of the light source. Preferably, the light guide is made of a transparent (including colorless and colored transparent) material. It is preferable that the light guide is made of a material which is easy to process and has excellent durability. As a material of the light guide, for example, acrylic resin, polyethylene terephthalate (PET), polycarbonate resin, epoxy resin, glass, or the like can be used.
[0012]
A light guide having a groove for accommodating a light source can also be employed. With this configuration, the light source and the light guide are integrally formed, so that the sealing performance is improved, and the light guide has a high dustproof and waterproof effect. The groove can be provided, for example, on the end face (upper end face, lower end face, or left and right end faces) of the light guide.
[0013]
Irregularities can be formed on the light emitting surface or the observation surface of the light guide. The irregularities reflect the light of the light source introduced into the light guide, and can promote irregular reflection and diffusion of light in the light guide.
The unevenness here includes a groove shape such as a triangular groove, a square groove, a round groove, and a pit shape. A plurality of irregularities having different shapes may be used in combination. Such irregularities can be formed continuously, or they can be formed discontinuously, such as in a dot shape. Further, they may be formed regularly or randomly.
Such an uneven portion can be formed by shaving a part of the surface of the light guide using a needle-shaped or saw-tooth-shaped processing tool, or by performing a cutting process, a polishing process, or the like on the surface of the light guide. Alternatively, such an uneven portion can also be formed by producing a light guide by molding using a mold that forms a desired uneven portion.
[0014]
A light diffusion layer is formed on the observation surface side of the light guide. The light diffusion layer is formed for the purpose of converting the light of the light source introduced into the light guide into light in the direction of the light emitting surface, and for equalizing the distribution of light in the light guide. In the light guide of the present invention, external light is controlled (diffused, etc.) by making the observation surface a convex curved surface. Therefore, it is not essential to provide a light diffusion layer for controlling external light.
The light diffusing layer is made of, for example, two or more light transmissive materials having different refractive indexes. Such a light diffusion layer has high transparency, and at the same time, enables good reflection and diffusion of light due to a difference in refractive index between constituent components. In terms of obtaining high transparency, the light guide of the present invention is particularly suitable for a front light. In addition, a moderate matting effect can be obtained by forming the light diffusion layer, and the occurrence of glare on the light guide surface can be further prevented or reduced. Also in this regard, the light guide of the present invention is extremely suitable for a front light.
The light diffusion layer as described above is formed of, for example, a material in which one or more particles made of a material having a different refractive index from the base material are mixed in a light-transmitting base material. A material having high light transmittance can be suitably used as the base material here. For example, an epoxy resin, an acrylic resin, a silicone resin, or a polycarbonate resin is employed. Two or more materials can be used as the material of the base material. On the other hand, the material of the particles to be mixed into the base material is not particularly limited as long as it has a high light transmittance and a refractive index different from that of the base material. For example, acrylic resin or glass can be used. The size (particle size) of the particles is not particularly limited, but if it is too large, the particles may be directly observed with the naked eye and the surface design of the light guide may be degraded. Therefore, the particle size of the particles is preferably smaller than the thickness of the light diffusion layer. As a more specific particle diameter, for example, the average particle diameter is 3 μm to 20 μm, and preferably 6 μm to 12 μm.
[0015]
Here, the particle content in the light diffusion layer is determined by the required light transmittance of the light diffusion layer, the degree of dispersion and application of the particles, the light transmittance of the substrate and the particles, and the required anti-glare. It can be determined in consideration of the degree of the effect and the like. For example, the base material: particles are 100: 1 to 100: 50, preferably 100: 10 to 100: 40 on a weight basis.
[0016]
Similarly, the thickness of the light diffusion layer can be determined in consideration of the required light transmittance of the light diffusion layer and the average particle diameter of the particles contained therein, for example, 1 μm to 50 μm, preferably 5 μm. ３０30 μm, more preferably 10 μm-20 μm. However, the thickness of the light diffusion layer is preferably larger than the average particle diameter of the particles contained therein. By doing so, the particles are easily buried in the light diffusion layer, and the surface of the light diffusion layer becomes smooth. The thickness of the light diffusion layer is preferably smaller than twice the average particle diameter. The relationship between the thickness (t) of the light diffusion layer and the average particle diameter (r) of the particles is represented by the following equation.
(Equation 1)
r <t <2r
By making the relationship between the thickness of the light diffusion layer and the average particle diameter in this way, the particles in the light diffusion layer are arranged side by side and one by one in a plane, and when a plurality of particles are formed in multiple stages, In comparison, diffuse reflection in the light diffusion layer is suppressed, and as a result, light is efficiently emitted from the light emitting surface. That is, light with higher luminance can be obtained.
The light diffusion layer is formed by a process such as printing, and has a substantially uniform thickness. Further, a light diffusion layer whose thickness increases continuously or stepwise as the distance from the light entrance surface of the light guide increases can be adopted. As it is expected that the amount of light reaching the light diffusion layer decreases as the distance from the light incident surface increases, and this is expected to cause uneven light distribution in the light guide, such a light diffusion layer is used. As a result, the reflection and diffusion efficiency can be enhanced in a region where the amount of light reaching is insufficient, so that the distribution of light in the light guide can be made uniform throughout. For the same purpose, when the light diffusion layer is composed of the base material and the particles as described above, the content of the particles in the light diffusion layer is continuously or gradually increased as the distance from the light incident surface increases. It can be.
[0017]
Silica or the like can be added to the light diffusion layer for the purpose of adjusting the viscosity of the forming material when forming the light diffusion layer or promoting good dispersion of the particles in the base material. For example, when silica or the like is added, a light diffusion effect can be obtained in addition to the above effects, that is, the reflection and diffusion effects of the light diffusion layer can be enhanced.
[0018]
In order to radiate light from the light emitting surface with less luminance unevenness, it is preferable to form a light diffusion layer on substantially the entire observation surface of the light guide. However, a light diffusion layer may be formed on a part of the observation surface of the light guide so that a predetermined pattern is formed in a plan view. The pattern here may be irregular, but in order to uniformly reflect and diffuse light over the entire light diffusion layer and thereby irradiate light with less luminance unevenness from the light emitting surface, It is preferable to adopt a typical one. Examples of the regular pattern include a pattern in which dots of a desired size are formed in a matrix, a slit-like pattern, a lattice-like pattern, and the like. In this case, the ratio of the area of the light diffusion layer to the observation surface is, for example, 30% to 90%. Preferably, it is 50% to 80%. By providing the light diffusion layer partially instead of the entire surface, an effect of preventing the observation surface from appearing white when light is incident on the observation surface from the outside can be obtained.
[0019]
It is preferable to form the light diffusion layer as long as it does not affect the transparency of the light guide. Preferably, the light diffusion layer is formed in a range where the light transmittance of the light guide does not become, for example, 80% or less. More preferably, the light diffusion layer is formed in a range where the light transmittance does not become 85% or less, further more preferably, in a range that does not become 90% or less. The light transmittance can be appropriately adjusted depending on the type and thickness of the light guide material to be used, the configuration (material, thickness, and the like) of the light diffusion layer.
[0020]
It is preferable to coat the observation surface of the light guide with a light transmissive material. That is, it is preferable to provide a protective layer on the observation surface. Thereby, the observation surface can be protected from dirt and scratches. Further, if such a coating is applied, the observation surface becomes a glossy surface, and the design of the light guide and the illumination target is improved. Furthermore, when a light-diffusing layer is provided, if a UV-absorbing material is used for coating, the light-diffusing layer can be protected from deterioration and damage due to ultraviolet light. Therefore, the function of the light diffusion layer is maintained for a long time.
The material of the protective layer is not particularly limited as long as it is transparent to light from the light source. Preferably, the protective layer is formed of a transparent material (including colorless and transparent). As the material of the protective layer, for example, acrylic resin, polyethylene terephthalate (PET), polycarbonate resin, epoxy resin, or the like can be used.
A light guide having a light diffusion layer and a protective layer on the observation surface can be manufactured by in-mold molding (film insert molding) using a film (light diffusion film) printed with light diffusion ink. . Hereinafter, an example of a procedure for manufacturing a light guide by in-mold molding will be described. First, a film base made of an appropriate material (for example, PMMA) is prepared, and light diffusing ink is printed on the surface thereof. As the light diffusing ink, a material used for forming the above light diffusing layer (a material in which one or more particles made of a material having a different refractive index from the light transmissive base material are mixed in the light transmissive base material) is used. be able to. The printing pattern is not particularly limited, and a dot shape, a slit shape, a lattice shape, or the like can be adopted. Next, the light-diffusing film prepared as described above is mounted on a mold such that the printed surface is on the light guide material side, and then the light guide material is injected into the mold. After cooling, the molded body in which the light diffusing film and the light guide are integrated is taken out from the mold. Through the above steps, a light guide is obtained in which a light diffusion layer composed of a print layer (print pattern) and a protective layer composed of a film base are sequentially laminated on the surface of the light guide. As a result, the observation surface becomes a glossy surface, and a light guide having excellent appearance design is obtained. In use, the design of the illumination object is also improved. It is preferable to use a light guide material having a lower melting point than a film-based material. This is because melting of the film base during injection molding can be prevented. Since the above-mentioned in-mold molding method is suitable for continuous production, its use is advantageous in mass production.
[0021]
When using the light guide of the present invention, it is preferable to bring the light guide close to the illumination target. This is because a higher illumination effect can be obtained, and the installation space can be reduced particularly when the light guide is fixed and used. For example, a light guide can be used with its light emitting surface in close contact with the illumination target. However, a layer or the like for promoting light diffusion may be interposed between the light emitting surface and the illumination target. For such a layer containing a light diffusing material, a sheet in which the light diffusing material is dispersed is attached to the light emitting surface of the light guide or the surface to be illuminated, or a resin containing the light diffusing material is applied. Can be formed by
[0022]
The light guide of the present invention is used as a planar or linear light source in combination with a light source. Here, as the light source, an LED, a light bulb (bulb), a fluorescent lamp, a cold cathode tube, or the like can be used. Among them, it is preferable to use an LED. The LED light source is a light source suitable for continuous lighting for a long time because of its low power consumption and small heat generation and long life. In addition, because of the small size, the space for the light source is small, and the planar light source of the present invention can be reduced in size and thickness. This also improves the handling of the planar light source. Further, since the LED is resistant to vibration and impact, there is an advantage that a highly reliable planar light source can be configured.
The type of the LED is not particularly limited, and various types such as a bullet type and a chip type can be adopted.
[0023]
The emission color of the light source used is not particularly limited, and a light source that emits light in a visible region such as white, red, orange, green, and blue can be used. Preferred light sources include those that emit white light. This is because if a light source that emits white light is adopted, it is possible to configure so that numbers, characters, figures, backgrounds, and the like displayed on the illumination target can be observed (visually recognized) in their original colors. On the other hand, if a light source of a color other than white is used, the design of the illumination target can be changed, for example, by adding color to the illumination target, or the design can be enhanced.
[0024]
A light source that emits light in the ultraviolet region can also be used. In this case, a phosphor that receives and emits light in the ultraviolet region can be used together. Note that a light source capable of emitting light in the visible region and the ultraviolet region may be used.
When a phosphor is used, for example, a layer containing the phosphor can be provided on the light guide surface (for example, the surface of the light emitting surface). Such a layer containing a phosphor can be formed by printing or applying a phosphor-containing ink or paint, or by attaching a sheet containing a phosphor. Further, a phosphor can be contained in the light guide. In such a configuration, fluorescent light is generated in the light guide, and the fluorescent light is emitted from the light emitting surface of the light guide to perform illumination. When the phosphor is contained in the light guide, it is particularly preferable to use an organic phosphor. If an organic phosphor is used, the transparency of the light guide can be maintained, and a clear lighting effect can be obtained.
[0025]
The phosphor can be contained not only in the surface light source but also in the object to be illuminated. For example, a display portion (numerals, characters, and the like) to be illuminated can be formed using a paint or ink containing a phosphor, or a layer containing a phosphor can be separately provided on the surface of the display portion. In such a configuration, light in the ultraviolet region emitted from the light source irradiates the illumination target via the light guide to excite the phosphor of the display unit. As a result, the display section to be illuminated emits light with fluorescent light.
[0026]
The kind of the phosphor is not particularly limited, and it can be adopted regardless of an organic type or an inorganic type. By using an organic phosphor, it is possible to obtain a fluorescent color light with a clear feeling as described above. On the other hand, when an inorganic phosphor is used, fluorescent light having a matte feeling can be obtained. Phosphors having various fluorescent colors can be employed.For example, phosphors having red, green, or blue fluorescent colors, which are the three primary colors of light, as well as phosphors that emit intermediate colors thereof can be used. . A plurality of phosphors can be used in combination. For example, a red phosphor, a green phosphor, and a blue phosphor can be mixed and used.
[0027]
The light source in the present invention may be configured using a plurality of LEDs, bulbs, and the like. In this case, a plurality of light sources of the same type can be used, or a combination of light sources having different emission colors can be used. By using a plurality of light sources, it is possible to obtain effects such as enhancement of illuminance or illumination of various luminescent colors by mixing colors of light. The number of light sources used can be determined by comprehensively considering the brightness of each light source, the size of the light guide, the required illuminance, and the like. As an example in which a plurality of light sources are used, for example, white light can be obtained using three types of red LED, green LED, and blue LED. In this case, a desired color of light can be obtained by controlling the light emission state and the light emission amount of each LED.
[0028]
The light source is arranged at a position where the light can be introduced into the light guide (light guide plate). It is preferable that the light source is arranged to face the end face of the light guide. In this way, the introduced light guides the inside of the light guide satisfactorily, and as a result, it becomes possible to irradiate light from a wider area of the light emitting surface of the light guide, and the light is emitted with less unevenness in illuminance. Irradiation. For example, one or a plurality of light sources can be arranged to face the upper end face, the lower end face, the left end face, and / or the right end face of the light guide. In particular, it is preferable to arrange the light source so as to face the upper end surface of the light guide. That is, it is preferable to irradiate the light guide from above to the lower end. In the case where the light diffusing process is performed on the observation surface of the light guide, for example, if the light of the light source is introduced from the lower end surface of the light guide, a large amount of light obliquely upward from the rear surface enters the observation surface, and from the front surface. Most of the light radiated to the outside is light traveling obliquely upward or upward. Here, when the light guide of the present invention is applied to lighting of a license plate of a vehicle, the viewpoint of an observer (for example, a driver of another vehicle) is usually located diagonally upward when viewed from the light guide. More light travels toward the viewpoint, and as a result, the observation surface of the light guide emits light and is observed more than the license plate, making the license plate difficult to see. On the other hand, if the light source is arranged above the light guide and light is introduced from the upper end of the light guide, most of the light emitted from the light guide observation surface becomes obliquely downward or downward light. Light traveling in the direction is small, and as a result, the phenomenon that the observation surface of the light guide emits light and the license plate becomes difficult to see as described above is prevented. The same effect can be obtained when the light source is arranged on the side of the light guide (either left or right end, or both left and right ends). However, when the light source is arranged above, the light source is closer to the observer's viewpoint. Since the amount of emitted light is small, it can be said that the position of the light source is most preferably above the light guide.
Here, as a specific example of the arrangement mode of the light source, there can be mentioned an embodiment in which a plurality of LEDs are linearly arranged in a state facing one end surface (preferably, the upper end surface) of the light guide. In such a mode, there is also an advantage that the configuration of a circuit used to light each LED can be simplified.
[0029]
Here, when the light amount of the light source is not sufficient, or when a sufficient light guiding action cannot be obtained, there is a concern that the distribution of light in the light guide (light guide plate) may be uneven. For example, the amount of light decreases in a region away from the light source, and as a result, illuminance unevenness may occur in light emitted from the light emitting surface of the light guide. In such a case, it is preferable to arrange the light sources such that light is introduced from both the upper and lower or left and right ends of the light guide. For example, a row of LEDs is arranged facing the upper end face of the light guide, and a row of LEDs is similarly arranged facing the lower end face of the light guide. Alternatively, one row of LEDs is used to face the left end face and the right end face of the light guide, respectively. Note that LEDs can be arranged on four sides so as to face the respective upper, lower, left, and right end surfaces. Further, LEDs can be arranged on three sides of the left and right end faces and the upper end face, or the left and right end faces and the lower end face.
It is preferable to arrange the light source close to the light guide from the viewpoint of light introduction efficiency and downsizing of the device.
[0030]
A light source and a cover covering the end face and the edge of the light guide may be provided. This cover is used to prevent the light source from being observed from the outside, to prevent light from leaking from the end face and the edge of the light guide, and to protect the edge of the light guide. You.
[0031]
Depending on the processing of the end face of the light guide, the leaked light may be almost negligible. Also, depending on the viewpoint, the observation of light from the end face (and / or edge) of the light guide has a decorative effect. Further, the light guide end face (and / or the edge) may be subjected to a cutting process or the like to create a light emitting mode in which a more decorative effect can be obtained. That is, light can be actively emitted from the end face (and / or edge) of the light guide, and this can be used for decorating the illumination target.
As described above, depending on the purpose of use and design of the light guide, it may not be necessary to hide the end face of the light guide, or it may be preferable to expose the end face of the light guide. Therefore, in such a case, a cover that covers only the light source instead of the cover as described above, a cover that covers only a part (for example, an upper end surface) of the end surface of the light source and the light guide, and the end surface of the light source and the light guide (For example, a top surface) and a cover that covers only an edge portion continuous with the top surface can be used.
[0032]
Illumination targets of the planar light source device of the present invention include, for example, a license plate of a vehicle, a liquid crystal monitor such as a PC (personal computer), an information transmission medium such as an indicating board and an advertisement (board) used outdoors or indoors, and Books and the like can be mentioned. Note that such an illumination target and the planar light source device of the present invention may be integrally configured.
[0033]
【Example】
Hereinafter, the configuration of the present invention will be described in more detail using examples. FIG. 1 is a perspective view showing a planar light source device 1 (hereinafter, referred to as “light source device 1”) for a front light according to an embodiment of the present invention. FIG. 2 is a sectional view taken along line AA of FIG.
The light source device 1 includes a light guide (light guide plate) 10 and a light source unit 20. The light guide 10 is made of an acrylic resin plate having a constant thickness. In the light guide 10, a pair of surfaces having the largest areas (the light emitting surface 12 and the observation surface 13) have a cubic curved shape (the light emission surface 12 is concave and the observation surface 13 is convex) except for the upper edge. . The shape of the observation surface 13 is a cubic curved surface (convex curved surface) protruding toward the center, and is symmetric with respect to the center line 17 as a symmetric axis. In addition, the region excluding the upper edge has vertical symmetry. The observation surface 13 is formed with a number of substantially triangular grooves that are continuous in a dotted line in the vertical direction so as to be staggered in the horizontal direction. The observation surface 13 is further coated with a light transmissive material over the entire region where the above-described grooves are formed, and the observation surface 13 is a glossy surface.
The innumerable grooves formed on the observation surface 13 are formed denser in a region away from the light incident surface (upper end surface) 11. Specifically, in a region closest to the light incident surface 11 side, a groove having a length of about 1.77 mm, a width of about 0.22 mm, and a depth of about 0.1 mm is formed at a pitch of about 0.5 mm in the vertical direction. Have been. The lateral pitch of the grooves is about 1.47 mm. On the other hand, near the center of the light guide 10, grooves having a length of about 1.62 mm, a width of about 0.21 mm, and a depth of about 0.08 mm are formed at a pitch of about 0.49 mm in the vertical direction. The lateral pitch of the grooves is about 1.16 mm. In the region farthest from the light incident surface 11, grooves having a length of about 1.26 mm, a width of about 0.22 mm, and a depth of about 0.06 mm are formed at a pitch of about 0.27 mm in the vertical direction. The lateral pitch of the grooves is about 0.36 mm.
Such a groove as described above can be formed by processing the light guide observation surface 13 so as to scratch it with a processing tool having a myriad of metal needles on its surface.
The surface of the light emitting surface 12 is mirror-like, while the surface of the light guide plate other than the light incident surface 11, the light emitting surface 12, and the observation surface 13 is roughened.
[0034]
A pedestal 23 whose upper surface is inclined is installed in a case 21 of the light source unit 20, and a plurality of LEDs 22 are mounted in a row on a substrate 24 mounted and fixed on the pedestal 23. The optical axis of each LED 22 arranged in this way passes through a substantially central area of the light guide 10. On the other hand, in order to efficiently introduce light, each LED 22 is designed to be arranged close to the light incident surface 11. In this embodiment, a total of eight LEDs 22 of a shell type and white light emission are used.
[0035]
A protection resistor and a control circuit are mounted on the substrate 24 in addition to the LEDs 22, and a wiring pattern for connecting the LEDs 22 in series is formed on the back surface thereof. Note that the LEDs 22 may be connected in parallel.
Electric power is supplied to the light source unit 20 via the wiring 25. The light source unit 20 is turned on and off by a switch 26 provided on the side surface of the case 21.
[0036]
In the light source device 1 having the above configuration, each LED 22 in the light source unit 20 is turned on by operating the switch 26, and emits white light. This white light is introduced into the light guide 10 via the light incident surface 11. The light guided through the light guide 10 is reflected and diffused by the grooves provided on the light guide observation surface 13. As a result, light is emitted toward the light emitting surface 12, and light is emitted through the surface. Further, the action of the groove promotes diffusion of light in the light guide 10. Here, as described above, since the grooves are formed so that the density increases as the distance from the light incident surface 11 increases, the more diffusely the light is diffused and diffused, the more efficiently the region is farther from the light incident surface 11. The light distribution in the light guide 10 is made uniform. Therefore, the light emitted from the light emitting surface 12 has extremely reduced illuminance (luminance) unevenness throughout.
In addition, by arranging the LEDs 22 so that the optical axis passes through a substantially central area of the light guide 10, the light of each LED 22 is guided well in the light guide 10 and reaches a distant place. As a result, the illuminance (luminance) of the light emitted from the light emitting surface 12 is made uniform. In particular, it is possible to prevent the illuminance of light emitted from the light emitting surface 12 near the light source unit 20 from becoming extremely high.
[0037]
On the other hand, when the light guide observation surface 13 is a cubic curved surface, light (indicated by L in FIG. 2) incident on the light guide 10 from the outside is reflected and diffused on the observation surface 13 in multiple directions. That is, a favorable light diffusion action occurs on the observation surface 13. As described above, in the light source device 1, a sufficient light diffusion effect can be achieved without providing a light diffusion layer that reduces the transparency on the surface of the light guide 10. Accordingly, a planar light source device having two characteristics required for a front light, that is, good light diffusion on the surface and high transparency is obtained.
[0038]
Next, a license plate lighting device 2 (hereinafter, referred to as “lighting device 2”) according to another embodiment of the present invention will be described. FIG. 3 is a perspective view showing the lighting device 2. FIG. 4 is a sectional view taken along line BB of FIG. In the following, the same members as those of the above-described planar light source device 1 are denoted by the same reference numerals, and description thereof will be omitted.
The illumination device 2 is roughly composed of a light guide (light guide plate) 30, an LED 22 mounted on a substrate 24, and a casing 40.
[0039]
As in the case of the light guide 10 in the above embodiment, the observation surface 33 of the light guide 30 has a tertiary convex curved shape that is symmetrical in the vertical and horizontal directions, and has a predetermined pattern of grooves formed therein. Further, a surface coating is applied (that is, the observation surface 33 is a glossy surface). On the other hand, the light emitting surface 32 of the light guide 30 is a flat surface, and the distance from the license plate 100 becomes equal during use as shown in FIG. 4 (actually, the light emitting surface 32 is It is in a state of being in close contact with the display surface).
The surface of the light emitting surface 32 is mirror-like, while the light guide surface other than the light incident surface 31, the light emitting surface 32, and the observation surface 33 is roughened.
[0040]
The casing 40 is a frame member made of resin, and has openings on the lower surface side and the rear surface side. Then, the upper end of the light guide 30 is covered, and the substrate 24 and the LED 22 are housed. The surface of the casing 40 may be subjected to plating treatment or painting treatment (for example, the same color as a bumper or garnish to be installed). Further, the casing 40 can be manufactured using a metal material. For example, the casing 40 can be formed by processing a metal plate into a frame shape and applying a coating on the surface thereof.
[0041]
The lighting device 2 is installed and fixed to the vehicle body 70 at the same time when the license plate 100 is mounted using the screws 50 and 51 (see FIG. 4). The screw 50 is sealed with a metal cap.
[0042]
Next, the lighting mode of the lighting device 2 will be described. First, power is supplied to each LED 22 in conjunction with the lighting of the vehicle width lamp (small lamp), and each LED 22 emits white light. This white light is introduced into the light guide 30 via the light incident surface 31. The light guided through the light guide 30 is reflected and diffused by a groove provided on the light guide observation surface 33. As a result, light is emitted toward the light emitting surface 32, and light is emitted through the surface. In addition, the action of the groove promotes the diffusion of light in the light guide 30 and the distribution of light over the entire light guide 30 makes the light emitted from the light emitting surface 31 less uniform. Illuminance (luminance) unevenness is significantly reduced over the whole. As a result, the light emitting surface 32 emits planar light whose luminance (illuminance) is uniform over the entire surface. As a result, the display surface of the license plate 100 is illuminated by the planar light (white light) with less illuminance unevenness, and the visibility of characters and numerals displayed there is effectively increased.
Here, since the distance between the light emitting surface 32 and the display surface of the license plate 100 becomes equal over the entire surface by making the light emitting surface 32 flat, after the light is emitted from the light emitting surface 32, the license plate 100 The degree of attenuation of light until reaching the display surface of the illumination light becomes equal over the entire illumination light, thereby enabling illumination with light with more uniform illuminance.
[0043]
On the other hand, by forming the observation surface 33 of the light guide 30 as a cubic curved surface, a sufficient light diffusion effect can be obtained on the observation surface 13 without providing a light diffusion layer for reducing the transparency on the surface of the light guide 30. Is done. That is, high transparency is ensured while providing good light diffusion on the surface, which is required for a front light. By providing good light diffusion on the surface, even when, for example, headlights of a following vehicle are incident, light reflected toward the occupant of the following vehicle is extremely reduced. Therefore, even in such a case, the visibility of the license plate 100 is sufficiently ensured, and the reflected light does not hinder the driving of the following vehicle. On the other hand, by providing the light guide 30 with high transparency, it is possible to satisfactorily recognize the characters and numbers on the license plate 100 even during illumination or during non-illumination such as during daytime (when the LED 22 is turned off). Become.
On the other hand, since the observation surface 33 of the light guide 30 is a glossy surface, not only the design of the light guide 30 itself is excellent, but also the design and visibility of the license plate illuminated thereby are extremely high. It will be.
[0044]
The present invention is not limited to the description of the embodiment of the present invention at all. Various modifications are included in the present invention without departing from the scope of the claims and within the scope of those skilled in the art.
[0045]
【The invention's effect】
In the light guide of the present invention, by forming the observation surface as a convex curved surface, a favorable light diffusion action by the observation surface itself occurs. Therefore, since it is not necessary to separately provide a light diffusion layer, high transparency can be ensured, which is suitable for front-light illumination.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a planar light source device 1 according to one embodiment of the present invention.
FIG. 2 is a sectional view taken along line AA in FIG.
FIG. 3 is a perspective view showing a license plate lighting device 2 according to another embodiment of the present invention.
FIG. 4 is a sectional view taken along line BB in FIG. 3;
[Explanation of symbols]
1 Planar light source device
2 License plate lighting device
10 30 Light guide (light guide plate)
12 32 Light guide light emitting surface
13 33 Light guide observation surface
20 light source unit
22 White LED
100 license plate

Claims (5)

A light incident surface, a light emitting surface that emits the introduced light to the outside, and an observation surface formed on the opposite side to the light emitting surface,
A light guide, wherein the observation surface has a convex curved shape. The light guide according to claim 1, wherein the convex shape is a third-order or higher-order curved surface shape. A planar light source comprising: the light guide according to claim 1; and a light source disposed to face the light incident surface of the light guide. 4. The planar light source according to claim 3, wherein the light source comprises an LED. A planar light source according to claim 3 or 4,
A license plate installed so that a display surface thereof faces the light emitting surface of the planar light source.

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